How to mount on Linux a QNAP external drive with LUKS partition

I need help to mount an external drive used on my QNAP TS-230 (latest firmware) to backup data. I set encrypted partition (LUKS) on this drive with a passphrase. I tried to mount that partition on a Linux system but when I enter the passphrase it doesn't work. I read the passphrase is hashed with the QNAP command storage_util --encrypt_pwd pwd= but I have the same problem with the string returned. Anyone have a solution? Thanks. I used the QNAP web interface to init the disk (*single partition, no others*), adding the encryption option. When I run sudo cryptsetup luksOpen /dev/sdb1 crypt_disk, it asks for the passphrase and the response is No key available with this passphrase.. I tried with both password: in clear, and wrapped with the command storage_util.